The present invention is concerned with a new, improved, and more stable colorimetric, diagnostic agent for the semi-quantitative determination of molybdate, ferric, and vanadate ions in cooling systems containing ethylene glycol or propylene glycol, or other solutions containing these ions. A further object of this invention is to provide a safe, rapid, and reliable means for testing for said ions. Another object of this invention is to produce a diagnostic test method possessing improved shelf life, useable over a wide sample temperature range (35.degree. F. to 180.degree. F.), useable over a wide pH range, and useable over a wide ion concentration range (10 to 4000 ppm).
Current test procedures using an absorbent support carrier (test strips) for detection of molybdate ions use dithiol or thiocyanate and tin chloride in the presence of acid for colorimetric detection. However, these methods require acid addition, use chemicals that are unpleasant in odor, are unstable, are sensitive to the presence of glycol or other interfering ions, or require several minutes for colorimetric development. It has now been found that all of the above disadvantages can be avoided by the use of this invention's stable, diagnostic test method which has a reaction time of approximately one minute.
Scientific periodicals have reported many organic hydroxy compounds that give satisfactory colorimetric reactions for determining micro-amounts of molybdenum with the use of gallic acid with cathecol, alizarin and O-hydroxycourmarins. These method require extraction to eliminate reactions with interfering ions. The formation of colorimetric complexes of molybdate ions with hydroxylamine and resorcinols, hydroxyphenols, butrylpyrogallol and gallic acid have been reported in aqueous media. However, the aqueous test solutions require mixing of reagents, pH adjustment, frequent reagent preparation due to instability, and a spectrophotometer for quantization. With the use of a suitable absorbent support or carrier, such as customarily employed for production of indicator test strips, the current invention overcomes the shortcomings of determining molybdate in aqueous media. Filter paper is most commonly employed as the absorbent support. Other absorbent support forms such as absorbent cellulose, cellulose derivatives, absorbent products such as polypropylene fiber and fiber glass laminates can likewise be used. In addition, film test strips can be made similar to film formulas identified in U.S. Pat. No. 3,630,957 or mixtures thereof but not limited to such film formulas.